One potential source of biofuels is to generate molecules from algae that are suitable for making fuels. For example, algae, like plants, can generate lipid molecules. Some lipid molecules have a general structure and molecular weight suitable for making diesel fuel additives such as fatty acid methyl ester (FAME). It is also possible to refine certain algae lipids into conventional fuels or fuel blending stocks including gasoline, diesel, and jet fuel. However, many challenges remain in developing commercial scale production techniques for biofuels based on algae production.
One challenge in developing algae based biofuels is recovering desired product molecules from the algae. Algae cells include a variety of components. In addition to desired lipids and/or other product molecules made by the algae, a typical algae cell will also include proteins and other compounds that form the cell walls and the internal structures of the cell. In order to recover desired products, the desired products need to be separated from the cell walls and other compounds in the algae. Additionally, algae are typically grown in a pond at dilute concentrations. Recovery of desired products from algae requires separation of the desired products from a substantial amount of water.
U.S. Pat. No. 7,868,195 describes systems and methods for extracting lipids from dewatered wet algal biomass. A sample of wet algae biomass is centrifuged or filtered to reduce the water content. This results in a sample with a solids content of 10% to 40%. The dewatered sample is then mixed with an amphiphilic solvent such as dimethyl ether or an alcohol, ketone, or aldehyde containing 1 to 4 carbons. The mixture can be optionally heated. Solids are removed by filtration, centrifugation, or decanting, and the amphiphilic solvent can be separated from the water and lipids by evaporation of the solvent. The remaining water and lipid mixture is then phase separated to recover the lipids.
International Publication WO 2010/104922 describes a method for algae biomass fractionation. The method includes adjusting the pH of an aqueous sample of algae (or other sample of algae with a water-based polar solvent) to condition the algae cell walls for release of desired products. The conditioned algae sample is then contacted with a non-polar solvent. The mixture is partitioned to separate the polar and non-polar solvents. Products are then recovered from both the polar and non-polar solvent portions.
U.S. Patent Application Publication 2011/0195085 describes methods for performing solvent extraction of lipids and proteins from algae using methods that preserve the food grade integrity of the products. The methods include using alcohols and other solvents in sequential extractions at temperatures up to the boiling point of the solvent. The methods appear to be performed at ambient pressure.